Combustion apparatus



April 12, 1955 R. T. M. FORMAN COMBUSTION APPARATUS Original Filed Feb. 7, 1949 Invenlor L & 3 M. I,

Attorneys United States Patent COMBUSTION APPARATUS Ronald Thomas Max Forman, Farnborough, England, assignor to Power Jets (Research and Development) Limited, London, England, a British company Original application February 7, 1949, Serial No. 75,042. Dividsd and this application April 12, 1951, Serial No. 220,6 5

Claims priority, application Great Britain January 4, 1949 3 Claims. (Cl. 6039.72)

This invention relates to combustion apparatus in which combustion is required to be supported by a current of air or other gas (hereinafter referred to as air) of flame extinguishing velocity. The term flame extinguishing velocity is usedto indicate that the mean speed of the combustion-supporting air current in its general direction of flow past a combustion zone, calculated from the ratio air volume passing in unit time/cross sectional area of flow path, is substantially higher than the speed of flame propagation in the fuel/air mixture concerned. For hydrocarbon fuels burning in air the speed of flame propagation is considered as being of the order of one foot per second at atmospheric temperature; the invention on the other hand, is especially applicable to combustion apparatus in which the speed of the air current in its general direction of flow past a combustion zone, calculated on the basis indicated, might be of an order as low as or as high as 500 feet per second or even more, depending upon the design.

An object of the invention is to avoid difficulties which arise when fuel has to be burnt in a flow of air through a duct whose cross-sectional area is large in the sense that having regard to the speed of flame propagation, the velocity of the air flow, and the length of passage available within which to complete combustion, it is not possible to achieve a spread of flame across the whole cross-section of the duct using only a single source of ignition.

In one aspect this invention is an improvement on that described in copending United States patent application Serial No. 220,610, for Combustion Apparatus, in the name of Johnstone. This application is a division of application Serial No. 75,042, filed February 7, 1949, now abandoned. In said application Serial No. 220,610, there is provided a combustion apparatus in which combustion is required to be supported by a gaseous stream of flame extinguishing velocity comprising a duct conveying said stream, a plurality of flame stabilizing means distributed over a transverse section of the duct, a plurality of fuel injecting means distributed over a transverse section of the duct upstream of the flame stabilizing means and injecting fuel without ignition into the duct, and means for controlling the lateral spread of the fuel between said fuel injecting means and flame stabilizing means. One method of limiting the spread of fuel is by enclosing the fuel injecting means by open ended tubular members having their axes parallel to that of the duct.

At high fuel pressures it is found that the fuel tends to escape at the upstream end of the tube and in this way the fuel may spread across the whole of the duct. An excessive length of tube would be required to prevent this and an object of the present invention is to limit such escape so that a local concentration of fuel in the duct may be obtained. This invention also makes it possible to produce a non-symmetrical distribution of fuel relative to the tubular member.

Accordingly the invention provides a combustion apparatus in which combustion is required to be supported by a gaseous stream of flame extinguishing velocity comprising a duct conveying said stream, flame stabilizing means located in said duct, fuel injecting means located in said duct upstream of said flame stabilizing means and injecting fuel without ignition into said duct, an open ended tubular member surrounding said fuel injecting means and having its axis parallel to that of the duct and an obturating member in said tubular member whereby theneslcape of fuel from the upstream end thereof is contro e The obturating member is preferably a plate located within the tubular member.

The invention is illustrated by accompanying drawing in which:

Figure l is a diagrammatic axial section of one form of the invention as applied to the burning of fuel in the exhaust pipe of a gas turbine jet propulsion unit.

way of example in the Figure 2 is an enlarged detail of the arrangement shown in Figure 1.

Figure 3 is an end view of the detail shown in Figure 2. i

In Figure l a turbine 1 has on its downstream side a fairing or bullet 2 forming with the exhaust cone 3 an annular diffusion passage. At the downstream end of this passage the jet pipe has a divergent section 4 which forms a further diffusion passage, and downstream of this there is a section 5 of constant cross-section terminating in a convergent portion 6 leading to a jet orifice 7. Fuel is in: ected upstream by a plurality of jets 9, located in an upstream portion of the diffusion passage 4, each of which jets is surrounded by an open ended tubular member 12 supported by a streamlined fairing 18 with its axis parallel to that of the duct. At the junction of the diffusion passage 4 and the section 5, there is provided a plurality of flame stabilizing baffles 10, each baflle being designed to.

9 and its corresponding baffle 10 is suflicient to allow timefor vaporization of the fuel, and the length of the tube 12 downstream of each jet 9 limits the lateral spread of fuel and hence a desired degree of concentration of the fuel-air mixture at the baffle 10 may be achieved.

The arrangement also prevents fuel from reaching the duct wall and causing local overheating. I

At low fuel pressures the fuel will remain within the tubular member 12, but at high pressures it will tend to escape at the upstream end. To control this escape an inclined plate 16 is mounted in the inner wall of the tubular member 12, the position and dimensions of this plate relative to the tubular member being selected to be such that the required control is effected. The plate may be adjustable both in regard to position and size for varying conditions of operation. As shown in Figure 2 part of the fuel is reversed by the plate and part escapes by the upstream end of the tubular member and is reversed by the air flow in the duct. In this way a non-symmetrical distribution of fuel relative to the tubular member may be achieved so that a desired concentration of fuel is caused in the neighbourhood of the baffles. In the particular case illustrated, the concentration of fuel is biased so as to be further from the duct wall than would otherwise be the case, so that the duct walls are not directly in contact with the flame.

I claim:

1. Combustion apparatus for burning fuel in a fastmoving gas stream comprising a duct carrying the stream and including a fuel injection and mixing zone and a flame zone spaced downstream therefrom, an open ended tubular member within the injection. and mixing zone of the duct and extending along the stream within this zone, a fuel injector within said tubular member arranged to direct a jet of fuel in an upstream direction, a baflie within said tubular member, lying in the path of said fuel jet and partly blocking the interior of the tubular member. a flame stabilizer spaced downstream from the tubular member and lying within the flame zone, and an igniter in the neighborhood of the flame stabilizer and within the flame zone.

2. Combustion apparatus for burning fuel in a fastmoving gas stream comprising a duct carrying the stream, a plurality of fuel injectors symmetrically disposed over one transverse section of the duct and each arranged to direct a jet of fuel in an upstream direction, a plurality of 3. Combustion apparatus according to claim 2 wherein open ended tubular members extending along the stream said plate is inclined to the axis of the tubular member. and each enclosing one of the injectors, a bafiie plate exltaeriding acrgass anl lpartly bltlaicking the iililterior of each References Cited in the file of this patent tu u at mem er an ying in t e path of t e fuel jet, the 5 plate being asymmetrically located with respect to the UNITED STATES PATENTS axis of the tubular member, being on that side of the said 2,506,611 Neal et al May 9, 1950 axis nearest to the duct well, a plurality of flame stabilizers 2,5 66,373 Redding Sept. 4, 1951 symmetrically disposed over a transverse section of the FOREIGN PATENTS duct spaced downstream from the tubular member and 10 a an lgniter in the neighborhood of said flame stabilizers. 920,910 France Jan. 8, 1947 

